I've never owned a mobile phone but am now considering buying one for emergency use only. I intend to use a Pay As You Go tariff.
Forgive my ignorance, but could someone answer the following for me:
1) I believe a mobile phone needs a 'Sim' Card.
What exactly is this and do I have to purchase it separately?
How do I fit it into the phone?
2) How do I top-up the phone at a supermarket etc.?
3) Is the top-up amount valid only for a set period or until the credit is exhausted no matter how long?